The present invention relates to a fuel feed system suitable for fuel feed to automotive engines and the like.
Typically, the fuel feed system mounted on vehicles such as automobile serves to feed fuel, such as gasoline, accumulated in a fuel tank to an engine main body through a fuel pump. Some fuel feed systems include an evapopurge apparatus for discharging fuel vapor evaporated in the fuel tank, i.e. evaporative emission, to the intake side of the engine (refer to JP-A 6-10777).
The evapopurge apparatus comprises a purge passage for evaporative emission extending from the fuel tank to an intake pipe of the engine. Provided to the purge passage are a canister having therein an adsorbent such as activated charcoal, a purge control valve for conducting communication and shutoff of the purge passage between the canister and the intake pipe, and an air introduction valve for introducing air into the canister when the purge control valve is opened. Here, the purge control valve and the air introduction valve are connected to an electronic control unit (ECU) for controlling the engine.
The ECU controls opening and closing of the purge control valve and the air introduction valve in accordance with engine operating conditions to temporarily accumulate in the canister evaporative emission generated in the fuel tank and discharge it into the intake pipe at appropriate timing.
In the event of trouble of the purge control valve or the air introduction valve or damage of the purge passage, evaporative emission may leak in the atmosphere even with discharge thereof stopped by the ECU.
Thus, in the earlier art, an air pump, a pressure sensor, and the like are provided to the purge passage so as to diagnose the gas-tightness thereof. Here, the air pump is connected to the purge passage between the canister and the purge control valve.
When diagnosing the gas-tightness of the purge passage, the purge control valve and the air introduction valve are closed to block the purge passage between the fuel tank and the purge control valve. Then, the air pump is operated to feed air into the blocked purge passage, increasing the pressure therein. Using the pressure sensor, the ECU checks a variation in the pressure within the purge passage. If the pressure is greatly reduced in a short time, it is determined that a leakage occurs in the purge passage, and thus is diagnosed that the system breaks down.